Study On Preparation Of Urea Formaldehyde Resin Microsphere

Polymer microspheres are spherical or other shaped particles withdiameter ranging from several nanometers to several microns, whichcomposed of polymer or polymer composites. With the development ofpreparation technique and relevant theories, a mature system has beenestablished for the preparation of all kinds of monodispersed polymermicrospheres between0.01and100μm. Now polymer microsphereshave been widely used in the coatings, cosmetics, plastic additive,photology and electronics fields for their huge specific surface area, goodsurface adsorptive property, adjustable structure and components,controllable particle size and shapes. Recently, as a special structuremicrosphere, microcapsules using polymer as shell and functionalmaterials as core have been successfully used for drug delivery andrelease, flexible display device and self-healing materials. In this article,we successfully prepared monodispersed poly(urea-formaldehyde)(PUF)and poly(melamine-formaldehyde)(PMF) microspheres by dispersionpolymerization. The formation mechanism and reaction conditions aresystematically investigated and discussed. The details are as follows:1. The sub-micron and monodispersed PUF and PMF microspheres were successfully prepared by dispersion polymerization using PVA asdispersing agent. The obtained PUF and PMF microspheres had a regularspherical shape, smooth surface and uniform size. For the PUFmicrosphere, we systematically discussed the influences of surfactants,assistants and other reaction conditions on morphology and sizedistribution of microspheres.2.“Dimple-like” and “bowl-like” PUF microspheres were preparedby dispersion polymerization of urea and formaldehyde in the aqueoussolution in the presence of nonionicsurfactants PVA and Span80. Theratios of PVA to Span80and reaction time were carefully designed toinvestigate the formation mechanism of the dimple-like and bowl-likemicrospheres.3. Microcapsules containing phthalocyanine blue(PB) E-ink weresuccessfully prepared by the one-step in situ polymerization of urea andformaldehyde. Pigments was refined by recrystallization to get200~500nm rod-like PB crystals. Octadecylamine was further used to modify thesurface and improve the dispersion in tetrachloroethylene of PB crystals.Scanning electron microscope(SEM) images showed that themicrocapsules had a regular spherical shape with a particle size of30~50μm and a smooth surface. The optimumconditions of preparation wereconfirmed as that: the mass ratio of surfactant poly(vinyl alcohol) to ureawas20%, reaction time was3~4h, pH value kept at3~4, and stirring rate was500~700rpm.